Fuel cell system including an ion filter

ABSTRACT

The present invention is directed to a fuel supply and fuel system with an ion filter and an ion gauge. The filter can be made from discrete pieces of polymeric filter material. The polymeric filter material is substantially the same as the proton exchange membrane or polymer electrolyte membrane (PEM) in the fuel cell. The ion gauge measures the level of ions in the fuel by measuring a voltage across a section of fuel or a current through the same section. The voltage or current is related to the ion level in the fuel.

FIELD OF THE INVENTION

This invention generally relates to fuel systems using fuel cells andfuel cartridges, and more particularly this invention relates to an ionfilter incorporated into such systems.

BACKGROUND OF THE INVENTION

Fuel cells are devices that directly convert chemical energy ofreactants, i.e., fuel and oxidant, into direct current (DC) electricity.For an increasing number of applications, fuel cells are more efficientthan conventional power generation, such as combustion of fossil fueland more efficient than portable power storage, such as lithium-ionbatteries.

In general, fuel cell technologies include a variety of different fuelcells, such as alkali fuel cells, polymer electrolyte fuel cells,phosphoric acid fuel cells, molten carbonate fuel cells, solid oxidefuel cells and enzyme fuel cells. Today's more important fuel cells canbe divided into three general categories, namely fuel cells utilizingcompressed hydrogen (H₂) as fuel, proton exchange membrane or polymerelectrolyte membrane (PEM) fuel cells that use methanol (CH₃OH), sodiumborohydride (NaBH₄), hydrocarbons (such as butane) or other fuelsreformed into hydrogen fuel, and PEM fuel cells that use methanol(CH₃OH) fuel directly (“direct methanol fuel cells” or DMFC). Compressedhydrogen is generally kept under high pressure, and is thereforedifficult to handle. Furthermore, large storage tanks are typicallyrequired, and cannot be made sufficiently small for consumer electronicdevices. Conventional reformat fuel cells require reformers and othervaporization and auxiliary systems to convert fuels to hydrogen to reactwith oxidant in the fuel cell. Recent advances make reformer or reformatfuel cells promising for consumer electronic devices. DMFC, wheremethanol is reacted directly with oxidant in the fuel cell, is thesimplest and potentially smallest fuel cell, and also has promisingpower application for consumer electronic devices.

DMFC for relatively larger applications typically comprises a fan orcompressor to supply an oxidant, typically air or oxygen, to the cathodeelectrode, a pump to supply a water/methanol mixture to the anodeelectrode and a membrane electrode assembly (MEA). The MEA typicallyincludes a cathode, a PEM and an anode. During operation, thewater/methanol liquid fuel mixture is supplied directly to the anode,and the oxidant is supplied to the cathode. The chemical-electricalreaction at each electrode and the overall reaction for a directmethanol fuel cell are described as follows:

Half reaction at the anode:CH₃OH+H₂O→CO₂+6H⁺+6e⁻

Half reaction at the cathode:O₂+4H⁺+4e⁻→2H₂O

The overall fuel cell reaction:CH₃OH+1.5O₂→CO₂+2H₂O

Due to the migration of the hydrogen ions (H⁺) through the PEM from theanode through the cathode and due to the inability of the free electrons(e⁻) to pass through the PEM, the electrons must flow through anexternal circuit, which produces an electrical current through theexternal circuit. The external circuit may be any useful consumerelectronic devices, such as mobile or cell phones, calculators, personaldigital assistants and laptop computers, among others. DMFC is discussedin U.S. Pat. Nos. 5,992,008 and 5,945,231, which are incorporated byreference in their entireties. Generally, the PEM is made from apolymer, such as Nafion® available from DuPont, which is aperfluorinated sulfonic acid polymer having a thickness in the range ofabout 0.05 mm to about 0.50 mm, or other suitable membranes.

The electrochemical cell reactions take place at a membrane electrodeassembly typically comprised of an anode diffusion layer, comprised of acarbon paper support treated with a fluoropolymer, such as Teflon®available from DuPont, an anode catalyst layer comprised of catalyst,such as platinum-ruthenium, and a proton conductor, such as Nafion®perfluorinated sulfonic acid polymer, the PEM, a cathode catalyst layercomprised of catalyst, such as platinum and a proton conductor and acathode diffusion layer comprised of a carbon paper support treated witha fluoropolymer.

The cell reaction for a sodium borohydride reformer fuel cell is asfollows:NaBH₄(aqueous)+2H₂O→(heat or catalyst)→4(H₂)+(NaBO₂)(aqueous)H₂2H⁺+2e⁻(at the anode)2(2H⁺+2e⁻)+O₂→2H₂O(at the cathode)Suitable catalysts include platinum and ruthenium, among other metals.The hydrogen fuel produced from reforming sodium borohydride is reactedin the fuel cell with an oxidant, such as O₂, to create electricity (ora flow of electrons) and water byproduct. Sodium borate (NaBO₂)byproduct is also produced by the reforming process. Sodium borohydridefuel cell is discussed in United States published patent application No.2003/0082427, which is incorporated herein by reference.

Cations other than protons reduce the conductivity of the PEM.Especially damaging to the membrane conductivity are multivalent metalions which tend to get trapped in the PEM. When the conductivity issufficiently reduced or when the level of trapped ions reaches athreshold level, the PEM has to be replaced or refurbished.

The patent literature discloses a number of filters for fuel cells. U.S.Pat. No. 6,265,093 B1 discloses a direct methanol feed fuel cell systemthat includes a fuel filter located in front the MEA. This filter is asieve-type filter that traps particles based on particle size to removehydrocarbon impurities from the fuel. U.S. Pat. No. 6,630,518 B1discloses a polymer membrane that is irradiated and then sulfonated tolink the sulfonic acid group to the membrane. The membrane is usable asthe PEM in fuel cells and is usable as ion-exchange member or inion-selective purification systems, among other uses.

Therefore, a need exists for a filter that reduces metal ionconcentration in fuel for use in a fuel cell.

SUMMARY OF THE INVENTION

The present invention is directed to an ion filter, which can bepositioned at any location in the fluidic system of a fuel cell.

The present invention is directed to a filter for use with a fuel cellcomprising an inlet, an outlet and a medium made from a perfluorinatedsulfonic acid polymer and disposed between the inlet and the outlet. Thefuel exiting the filter contains less metal ion particles than fuelentering the filter. The perfluorinated sulfonic acid polymeric mediumis substantially similar to the polymer electrolyte membrane or protonexchange membrane in the membrane electrode assembly of the fuel cell.

The filter can be connected to a fuel supply or to a fuel cellcomponent. The filter may also have a housing that encases the filtermedium, and the filter medium can be shredded or can be in the form ofingots to increase the surface area of the medium.

The present invention is further directed to a fuel supply for a fuelcell comprising an outer casing containing fuel with a first amount ofions therein, and an ion filter supported by the casing. The ion filteris in fluid communication with fuel so that the fuel exiting the ionfilter has a second amount of ions less than the first amount of ions.This ion filter is substantially similar to the ion filter describedabove.

The present invention is also directed to a perfluorinated sulfonic acidpolymer filter medium adapted to attract metal ions from fuel usable ina fuel cell and from liquid byproduct produced in the fuel cell. Thefilter medium is substantially similar to the polymer electrolytemembrane in the membrane electrode assembly of the fuel cell, and thefilter medium is positioned within the fluidic flow path related to thefuel cell, e.g., the fuel cartridge, the mixing chamber and/or thebyproduct chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which form a part of the specification andare to be read in conjunction therewith and in which like referencenumerals are used to indicate like parts in the various views:

FIG. 1 is a schematic view of a fuel cell system with a fuel cartridge,an ion filter and ion gauge in accordance with the present invention;

FIG. 2 is an enlarged, partial cross-sectional view of a portion of thefuel cartridge of FIG. 1 with the ion filter and a gage for measuringion level in the fuel; and

FIG. 3 is a partial schematic view of another embodiment of the fuelcell system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in the accompanying drawings and discussed in detailbelow, the present invention is directed to a fuel supply, which storesfuel cell fuels such as methanol and water, methanol/water mixture,methanol/water mixtures of varying concentrations or pure methanol.Methanol is usable in many types of fuel cells, e.g., DMFC, enzyme fuelcell, reformat fuel cell, among others. The fuel supply may containother types of fuel cell fuels, such as ethanol or alcohols, chemicalsthat can be reformatted into hydrogen, or other chemicals that mayimprove the performance or efficiency of fuel cells. Fuels also includepotassium hydroxide (KOH) electrolyte, which is usable with metal fuelcells or alkali fuel cells, and can be stored in fuel supplies. Formetal fuel cells, fuel is in the form of fluid borne zinc particlesimmersed in a KOH electrolytic reaction solution, and the anodes withinthe cell cavities are particulate anodes formed of the zinc particles.KOH electrolytic solution is disclosed in United States published patentapplication No. 2003/0077493, entitled “Method of Using Fuel Cell SystemConfigured to Provide Power to One or more Loads,” published on Apr. 24,2003, which is incorporated herein by reference in its entirety. Fuelsalso include a mixture of methanol, hydrogen peroxide and sulfuric acid,which flows past a catalyst formed on silicon chips to create a fuelcell reaction. Fuels also include aqueous sodium borohydride (NaBH₄) andwater discussed above. Fuels further include hydrocarbon fuels, whichinclude, but are not limited to, butane, kerosene, alcohol and naturalgas, disclosed in United States published patent application No.2003/0096150, entitled “Liquid Hereto-Interface Fuel Cell Device,”published on May 22, 2003, which is incorporated herein by reference inits entirety. Fuels also include liquid oxidants that react with fuels.The present invention is, therefore, not limited to any type of fuels,electrolytic solutions, oxidant solutions or liquids contained in thesupply. The term “fuel” as used herein includes all fuels that can bereacted in fuel cells or in the fuel supply, and includes, but is notlimited to, all of the above suitable fuels, electrolytic solutions,oxidant solutions, liquids, and/or chemicals and mixtures thereof.

As used herein, the term “fuel supply” includes, but is not limited to,disposable cartridges, refillable/reusable cartridges, containers,cartridges that reside inside the electronic device, removablecartridges, cartridges that are outside of the electronic device, fueltanks, fuel refilling tanks, other containers that store fuel and thetubings connected to the fuel tanks and containers. While a cartridge isdescribed below in conjunction with the exemplary embodiments of thepresent invention, it is noted that these embodiments are alsoapplicable to other fuel supplies and the present invention is notlimited to any particular type of fuel supplies.

In accordance with one aspect of the present invention, the fuel cellsystem possesses an ability to filter the fuel to significantly reducethe metal ion particles in the fuel. As illustrated in the accompanyingdrawings and discussed in detail below, the present invention isdirected to a fuel cell 10 for powering electronic device 11.

FIG. 1 illustrates one embodiment of the present invention and the fuelcell system contains two sets of connecting lines. The first set ofconnecting lines comprises fluid, i.e., liquid and gas, lines, whichhave arrows to show the direction of flow. The second set of connectinglines comprises electrical lines, which have darkened circles at theintersections to show electrical connectivity. While this embodiment isdescribed with respect to direct methanol fuel cell, it is understoodthat this embodiment is suitable for any fuel cell.

Cartridge 12 is connected to fuel cell 10, which powers electronicdevice 11. Cartridge 12 can be formed with or without an inner liner orbladder. Cartridges without liners and related components are disclosedin co-pending U.S. patent application Ser. No. 10/356,793, entitled“Fuel Cartridge for Fuel Cells,” filed on Jan. 31, 2003. The '793application is incorporated herein by reference in its entirety.Cartridges with inner liners or bladders are disclosed in co-pendingU.S. patent application Ser. No. 10/629,004, entitled “Fuel Cartridgewith Flexible Liner,” filed on Jul. 29, 2003. The '004 application isalso incorporated herein by reference in its entirety. The fuel cellsystem shown in FIG. 1 is fully described in co-pending U.S. patentapplication entitled “Fuel Cell System including Information StorageDevice and Control System,” filed on even date herewith. This co-pendingapplication is incorporated herein by reference in its entirety.

Electronic device 11 is typically larger than fuel cell 10 and usuallyhouses the fuel cell. In FIG. 1, electronic device 11 is shownschematically to surround fuel cell 10. It is also represented by a boxdrawn by broken lines and is powered by the electrical current producedby MEA 16. The electrical device can also be a charger that rechargesbatteries.

With respect to the fluidic circuit, the fuel cartridge is connected tovalve 24, which preferably is a two-component valve. Valve component 24a is attached to the cartridge and valve component 24 b is connected topump 14. Each valve component is capable of forming a seal when the fuelcartridge is separated from the fuel cell. Two component valves arefully disclosed in co-pending patent application Ser. No. 10/629,006entitled “Fuel Cartridge with Connecting Valve,” filed on Jul. 29, 2003.This patent application is also incorporated herein by reference in itsentirety.

Inside fuel cell 10, valve component 24 b may directly connect to pump14 and provides a seal for pump 14, when the fuel cartridge isdisconnected. Alternatively, valve component 24 b may be attached toother fuel cell components. Pump 14 is connected to optional valve 252,which functions as a flow regulating device, and the flow rate throughpump 14 and valve 252 can be measured with flow meter 254, such as aVenturi meter or other electronic flow meters. Fuel is then pumped intomixing chamber 250. From mixing chamber 250, fuel/water mixture is pumpdirectly to MEA 16 to generate electricity to power electrical device11. Liquid and gas byproducts, e.g., water and carbon dioxide, can bepumped or flowed under pressure from the carbon dioxide gas to byproductchamber 256. The water byproduct is then transported back to mixingchamber 250. Mixing chamber 250 has relief valve 258 to vent the gasbyproduct and excess water outside the fuel cell. Relief valves can bepoppet-type valve disclosed in the '004 application. The water is mixedwith fuel in mixing chamber 250 to achieve an optimal fuelconcentration. Fuel concentration is measured by fuel concentrationsensor 260, and these sensors are disclosed in United States patentpublication Nos. 2003/0131663 and 2003/0134162 and in U.S. Pat. Nos.6,254,748 and 6,306,285. These references are incorporated by referenceherein.

When pressurized fuel supplies are used, pump 14 may be omitted. In thisembodiment, regulating valve 252 regulates the flow of fuel to MEA 16.Regulating valve 252 is fully disclosed in co-pending patent applicationentitled “Fuel Cell System including Information Storage Device andControl System.”

Alternatively, the byproducts, except for the water required for thefuel cell reaction, are transferred back to fuel cartridge 12 fordisposal. Relief valve 258 can be disposed on the fuel cartridge to ventthe gas byproduct to atmosphere. Furthermore, byproduct chamber 256 canbe omitted and the byproducts are transported directly from MEA 16 tomixing chamber 250. In an alternative embodiment, chamber 250 can bedivided into two portions as illustrated by the broken line in chamber250. Chamber 250 a is adapted to receive fuel from the fuel cartridgeand chamber 250 b is adapted to receive the byproducts. Each chamber 250a and 250 b is individually connected directly to MEA 16 or to anothermixing chamber upstream of the MEA. Each chamber 250 a, 250 b can beindividually connected to a pump, e.g., pump 262, to regulate the flowfrom each chamber to the MEA to obtain optimal fuel concentration.

With respect to the control circuit, which is fully discussed inco-pending patent application entitled “Fuel Cell System includingInformation Storage Device and Control System,” controller 18 is setupto control the flow of fuel through the fuel cell. Controller 18 can bepositioned within fuel cell 10 or in electronic device 11. Thecontroller can also be positioned on the fuel cartridge, or thefunctions of the controller can be performed by the central processingunit (CPU) or controller of the electronic device 11. Controller 18 canread information stored on information storage devices 23, 266, 268 andwrite information to these information storage devices. Controller 18can also read electrically readable fuel gauge 264 to ascertain theamount of remaining fuel. Such gauge is disclosed in co-pending patentapplication Ser. No. 10/725,236, entitled “Fuel Gages for FuelCartridges,” filed on even date herewith, which is incorporated hereinby reference in its entirety. Controller 18 can also be connected totwo-component valve 24, so that the controller can control the openingand closing of valve 24. The controller can also read sensors, such asflow meter 254, fuel concentration sensor 260 and ion sensor 272.

Controller 18 can also set the pumping rate of pump 14 or how wideregulating valve 252 should be opened to control the flow rate. Thecontroller is also connected to optional pump 262, which pumps fuel orfuel mixture from mixing chamber 250 to the MEA, to control the flowrate. Optionally, another regulating valve, similar to valve 252, isconnected to pump 262 to control the flow rate.

In accordance with one aspect of the present invention, an ion filter isprovided to fuel cell 10 and/or cartridge 12. With reference to FIG. 2,an enlarged view of filter 270 within outlet 22 of the cartridge isshown. Filter 270, in this preferred embodiment, comprises a Nafion®perfluorinated sulfonic acid polymer (available from DuPont). Since ionparticles are known to permeate and reduces the effectiveness of Nafion®polymers used as the PEM in the MEA, when the filter material is madefrom the substantially same material as the PEM and the filter islocated upstream of the MEA, the ion particles would be attracted to thefilter and be removed from the fuel before the fuel reaches the MEA.Hence, the filter material is selected to be substantially the same asthe PEM material.

In the present embodiment, the polymer material is shredded intodiscrete pieces or be made into ingots 270 a that are packed together toform filter 270. Providing a filter material of discrete piecesincreases the surface area of the filter material exposed to the fuel Fso that the filter can be compact and effective. Alternatively, thefilter material can be provided in a fine powder or the like. In thepresent embodiment, the discrete polymer pieces 270 a are bound togetherin an optional binder 270 b. Suitable binders 270 b should be resistantto the fuel used. Alternatively, instead of a binder, the filtermaterial can be contained within an open mesh fuel-resistant grid suchas the matrix disclosed in co-pending '004 patent application.

The metal ions in the fuel are absorbed or attracted to the filtermaterial within the filter via diffusion so that the fuel F′ exiting thefilter has a second amount of ions less than the first amount of ions inthe entering fuel F. Diffusion allows the filter material to collections when fuel flows through the filter, while requiring a relativelysmall pressure drop across the filter. Filter 270 does not discriminatebased on particle size, and therefore is a non-sieve filter.

The density and permeability of the filter material in filter 270determine the flow characteristics of the fuel F through the filter.Preferably, the filter material is wetted before it is assembled intothe cartridge so that it expands to between about 5% to about 25% of itsinitial volume. More preferably, the filter material is wetted to expandto about 15% of its initial volume.

The filter material may include the one or more catalysts, such asplatinum and/or ruthenium that are “unsupported,” i.e., without a basematerial. Again, the filter material can be shredded or provided in afine powder and used as previously discussed. The polymeric filtermaterial can also be extruded to form a textile mat including woven andnonwoven, which is the disposed in the fuel flow path.

Filter 270 when disposed in nozzle 22, as shown in FIG. 2, is downstreamof the fuel supply and upstream of pump 14. Preferably, pump 14transports fuel from the fuel supply and through the filter underpressure. Alternatively, as shown in FIG. 3, filter 270 is locateddownstream of fuel cartridge 12 and pump 14. Filter 270 may includediscrete pieces 270 a of filter material contained within housing 274.Housing 274 has inlet 276 and outlet 278. Preferably, housing 274 ismade from a fuel compatible material. The filter can also be located onthe cartridge. Additionally, when both filter 270 and the shut-off valveare located in nozzle 22, filter 270 also acts as a flow regulator toslow down the flow of fuel when the shut-off valve opens. Such a use ofthe filter and shut-off valves are fully disclosed in the co-pending'006 patent application incorporated by reference above. As a flowregulator, the filter can be positioned upstream or downstream from theshut-off valve.

Referring again to FIG. 1, in accordance to another aspect of thepresent invention, ion sensor 272 is provided to ascertain theeffectiveness of the filter and to determine when the filter should bereplaced. Ion sensor 272 is preferably located within fuel cell 10 asshown, or be disposed on the fuel cartridge. Ion sensor 272 iselectrically connected with controller 18, and is readable by thecontroller. Ion sensor 272 applies an electrical field to the fuel,e.g., across the tube carrying fuel or within the tube, as illustratedin FIG. 2. This electrical field is either a constant voltage across thefuel or a constant current though the fuel. The electrical conductivityof the fuel depends on the concentration of ion particles in the fuel.The ion population is directly proportional to either the currentflowing through the fuel if a constant voltage is applied across thefuel or the voltage across the fuel if a constant current is flowingthrough the fuel. A real-time ion measurement is compared to a base-linemeasurement of low ion fuel to determine whether the ion level isacceptable. Alternatively, a calibration curve or table can be drawnfrom data points representing low ion level, unacceptable ion level andone or more points therebetween. The real-time measurement can becompared to this calibration curve to ascertain the ion level duringuse. Controller 18 periodically reads this voltage or current and whenthe voltage or current reaches a predetermined level, the controllerdisplays a message or other signal such as a visual or audible signal,to the user to change the ion filter, possibly at the next refill of thefuel supply.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objectives of the present invention, it isappreciated that numerous modifications and other embodiments may bedevised by those skilled in the art. Additionally, feature(s) and/orelement(s) from any embodiment may be used singly or in combination withother embodiment(s). For example, filter material can be placed withincartridge 12, mixing chamber 250 and/or byproduct chamber 256 to extractmetal ion particles from the fuel and/or water byproduct. Therefore, itwill be understood that the appended claims are intended to cover allsuch modifications and embodiments, which would come within the spiritand scope of the present invention.

1. A filter for use with a fuel cell comprising: an inlet, an outlet,and a medium made from perfluorinated sulfonic acid polymer and disposedbetween the inlet and the outlet, wherein fuel exiting the filtercontains less metal ions than fuel entering the filter, wherein theperfluorinated sulfonic acid polymer is substantially similar to apolymer electrolyte membrane in the fuel cell and includes at least onecatalyst.
 2. The filter of claim 1 being connectable to a fuel supply.3. The filter of claim 1 being positioned in a fuel supply.
 4. Thefilter of claim 1 being connectable to a fuel cell.
 5. The filter ofclaim 1 being positioned in a fuel cell.
 6. The filter of claim 1 beingpositioned in an electronic device powered by a fuel cell.
 7. The filterof claim 1 further comprising a housing encasing the medium.
 8. Thefilter of claim 1, wherein the perfluorinated sulfonic acid polymermedium is shredded.
 9. The filter of claim 1, wherein the perfluorinatedsulfonic acid polymer medium is in the form of ingots.
 10. The filter ofclaim 1, wherein the perfluorinated sulfonic acid polymer medium is madeinto a textile web.
 11. The filter of claim 10, wherein the textile webis a nonwoven web.
 12. The filter of claim 10, wherein the textile webis a woven web.
 13. The filter of claim 1, wherein the perfluorinatedsulfonic acid polymer medium is made into powder form.
 14. The filter ofclaim 1, wherein the medium is wetted before use.
 15. The filter ofclaim 1 operatively connected to a sensor to measure the electricalconductivity of the fuel.
 16. The fuel supply of claim 11, wherein theat least one catalyst is unsupported by a base material.
 17. The filterof claim 1, wherein the at least one catalyst comprises platinum orruthenium.
 18. A fuel supply for a fuel cell comprising: an outer casingcontaining fuel with a first amount of ions therein, and an ion filtersupported by the casing, said ion filter is in fluid communication withsaid fuel, said ion filter comprises a filter material made from aperfluorinated sulfonic acid polymer and at least one catalyst and thefilter material is substantially similar to a polymer electrolytemembrane in the fuel cell; wherein upon flowing said fuel through saidion filter, the fuel exiting the ion filter has a second amount of ionsless than said first amount of ions.
 19. The fuel supply of claim 18,wherein the ion filter includes discrete pieces of the filter material.20. The fuel supply of claim 18, wherein the filter material isshredded.
 21. The fuel supply of claim 18, wherein the filter materialis wetted before use.
 22. The fuel supply of claim 18 operativelyconnected to a sensor to measure the electrical conductivity of thefuel.
 23. The fuel supply of claim 18, wherein the at least one catalystis unsupported by a base material.
 24. The fuel supply of claim 18,wherein the at least one catalyst comprises platinum or ruthenium.